Universal joints, and especially constant velocity joints, operate to transmit torque between two rotational members. A cage, or yoke, that allows the rotational members to operate with their respective axes at a relative angle, typically interconnects the rotational members. Constant velocity joints and similar rotating couplings typically include a flexible boot to enclose and protect the coupling during operation. The boot seals lubricant within the joint so as to reduce friction and extend the life of the joint. The boot also seals out dirt, water and other contaminants to protect the functionality of the joint. In addition, because the boot is typically flexible, the boot is able to seal around the joint while permitting articulation and relative angular movement of the rotational members.
Universal joints are commonly classified by their operating characteristics. One important operating characteristic relates to the relative angular velocities of the two connected rotational members or shafts. In a constant velocity type of universal joint, the instantaneous angular velocities of the two shafts are equal, regardless of the relative angular orientation between the two shafts. In a non-constant velocity type of universal joint, the instantaneous angular velocities of the two shafts vary with the angular orientation (although the average angular velocities for a complete rotation are equal). Another important operating characteristic is the ability of the joint to allow relative axial movement between the two shafts. A fixed joint does not allow this relative movement, while a plunge joint does allow this movement.
A typical constant velocity universal joint includes a cylindrical inner race that is connected to one of the rotational members or shafts and a hollow cylindrical outer race that is connected to the other of the rotational members or shafts. In one such example, the outer surface of the inner race and the inner surface of the outer race each have a plurality of grooves formed therein. Each groove formed in the outer surface of the inner race is associated with a corresponding groove formed in the inner surface of the outer race. A ball or torque-transmitting member is disposed in each of the associate pairs of grooves. The balls provide a driving connection between the inner and outer races. An annular cage is typically provided between the inner and outer races for retaining the balls in the grooves. The cage is provided with a plurality of circumferentially spaced openings for this purpose. In a typical plunge joint, the connection between the cylindrical inner race and the rotational member or shaft is a splined connection to permit relative axial translation between the cylindrical inner race and the shaft.
FIG. 1 illustrates a prior art plunge boot 10. Plunge boot 10 has a frusto-conical shaped elongated body to accommodate axial movement with a plunge CVJ. Plunge boot 10 is molded in a frusto-conical shape for ease of manufacture that reduces costs associated with molding.
To install plunge boot 10 on a CVJ, plunge boot 10 must be manipulated into a predetermined installed configuration. In prior art plunge boot designs, plunge boot 10 includes a large end 12 that is inverted over a middle portion 14 when installed and operated. The inversion, or folding, of the prior art plunge boot 10 forms a curve in portion 16 of the boot 10. However, the inversion of the prior art plunge boot 10 induces undesirable stress and strain in the portion 16. During operation, the plunge boot 10 may fail in the portion 16 due to these induced, post manufacture, stresses.
Another disadvantage of the prior art plunge boot 10 is that the inversion may create a wrinkling within the contour of the boot. The wrinkling provides additional stress points for failure to occur. Therefore, a boot is needed that can accommodate axial extension, but minimizes induced stresses when installed on the joint assembly.